Module 7 - Other Sensory Systems

What does the auditory system transduce?

Sound energy into neural activity.

How is mechanical energy generated in the auditory system?

By the vibration of air molecules stimulating hair cells.

What is the human hearing range?

20–20,000 Hz.

What is the best hearing range for humans?

3,000–4,000 Hz.

What three properties define sound waves?

Amplitude (loudness), frequency (pitch), and complexity (timbre).

What is timbre?

The perception of sound complexity or the presence of multiple frequencies at once

How is sound loudness measured?

In decibels (dB) as sound pressure level.

What are pure tones, and where do they occur?

Simple sine waves that occur only in lab settings; not natural.

Why can’t pure tones be localized?

Because they lack complex patterns and cues used by the auditory system to locate sound.

What is Fourier analysis?

A mathematical method to decompose complex waves into component sine waves of different frequencies and amplitudes.

What is the Fourier theory of hearing?

The auditory system performs Fourier analysis, breaking down complex sounds into component frequencies.

What is tonotopic organization?

The systematic mapping of sound frequency across the auditory system.

What is a neural tuning curve?

A graph showing a neuron’s response to different frequencies and intensities.

What is a characteristic frequency (CF)?

The frequency to which a neuron responds most strongly.

What is the pathway of sound through the outer ear?

Sound waves → auditory canal → tympanic membrane → ossicles → oval window.

What are the three ossicles and their functions?

Malleus (hammer), incus (anvil), stapes (stirrup); they transfer and amplify vibrations from the eardrum to the cochlea.

What does the cochlea do?

Converts mechanical vibrations into neural signals through the organ of Corti.

What are the three main chambers of the cochlea?

Scala vestibuli, scala tympani (both contain perilymph), and scala media (contains endolymph).

What is the organ of Corti?

The auditory receptor organ that contains hair cells and the tectorial membrane.

How does sound travel in the cochlea?

Vibrations enter via the oval window, travel through fluid-filled chambers, and dissipate through the round window.

What is the function of the basilar membrane?

It holds the hair cells that transduce sound vibrations.

What is the function of the tectorial membrane?

It rests on hair cells and moves with sound waves, bending the cilia to trigger neural activity.

What determines where sound frequencies are processed in the cochlea?

High frequencies stimulate hair cells near the base (oval window); low frequencies near the apex (tip).

What fluid surrounds hair cells and why is it important?

Endolymph, rich in potassium (K+); the ionic imbalance provides energy for transduction.

How do hair cells transduce mechanical energy?

Movement of the tectorial membrane bends cilia, opening K+ channels via tip links, leading to depolarization and neurotransmitter release.

What happens when hair cells move toward the smallest cilium?

K+ channels close, causing hyperpolarization and decreased activity.

What are tip links?

Thread-like connections between cilia that open cation channels when stretched.

What is the role of outer hair cells?

Receive efferent input from the brain to amplify or modulate sound sensitivity (cochlear amplifier).

What is the role of inner hair cells?

Primary sensory transducers that send signals to the auditory nerve.

How many more outer hair cells are there compared to inner hair cells?

Approximately three times more.

What are otoacoustic emissions?

Sounds generated by outer hair cells that can be recorded in the ear canal—signs of normal hearing.

What is the first structure to receive auditory nerve input?

The ipsilateral cochlear nucleus.

What structure combines signals from both ears?

The superior olives.

What are the next major relay stations in order?

Inferior colliculus → medial geniculate nucleus (MGN) of the thalamus → primary auditory cortex (A1).

Is auditory processing contralateral or ipsilateral?

Mostly contralateral but with bilateral input at many stages.

Where does sound localization occur?

In the superior olives.

What do the medial superior olives detect?

Interaural time differences (differences in timing between ears).

What do the lateral superior olives detect?

Interaural level differences (differences in loudness between ears).

How do superior olives communicate spatial information?

Project to superior colliculi, aligning auditory and visual maps of space.

Where is the primary auditory cortex (A1) located?

Temporal lobe within the lateral fissure on Heschl’s gyrus.

What is A1’s organization?

Tonotopic; low frequencies are lateral, high frequencies are medial.

How does A1 differ from A2?

A2 (belt area) responds to more complex and variable sounds.

What does the parabelt region process?

Even more complex sounds like speech or species-specific vocalizations.

How is the auditory cortex hierarchically organized?

From simple (A1) to complex (A2 and beyond).

What happens after auditory cortex damage?

Temporary hearing loss, but hearing usually recovers within weeks

What deficits may remain after damage?

Problems with sound localization or frequency discrimination

What is conductive deafness?

Hearing loss caused by ossicle damage.

What is nerve deafness?

Damage to the cochlea or auditory nerve, often from loss of hair cells.

Which frequencies are typically lost first with age-related deafness?

High frequencies.

How do hearing aids help?

They amplify sound to compensate for reduced sensitivity.

What do cochlear implants do?

Convert sound into electrical signals that directly stimulate the auditory nerve, bypassing damaged hair cells.

Why is early cochlear implantation beneficial?

Due to neural plasticity—better adaptation when done early

What is gustation?

The sense of taste; the process by which chemical molecules from food and drink are detected and interpreted.

What are the five basic taste qualities?

Sweet, sour, salty, bitter, and umami (savory).

What is the function of sweet taste?

Signals the presence of carbohydrates and energy-rich nutrients.

What is the function of sour taste?

Detects acids, helping identify potentially spoiled or unripe food

What is the function of salty taste?

Detects sodium, essential for maintaining electrolyte balance.

What is the function of bitter taste?

Acts as a warning system for toxins or poisonous substances.

What is the function of umami taste?

Detects glutamate and amino acids, indicating protein-rich foods.

What are taste buds?

Receptor structures containing taste receptor cells, located mostly on the tongue within papillae.

Where are taste buds located?

Mainly on the tongue (in papillae), but also on the soft palate, cheeks, and throat.

How many taste buds do humans have?

Approximately 5,000–10,000.

What are the types of papillae on the tongue?

Fungiform, foliate, circumvallate, and filiform (which do not contain taste buds).

How do taste receptor cells function?

They detect chemical molecules dissolved in saliva and send signals to sensory neurons.

What cranial nerves transmit taste information?

Facial (VII), glossopharyngeal (IX), and vagus (X) nerves.

Where is taste processed in the brain?

Signals travel from the tongue → medulla → thalamus → gustatory cortex (in the insula and frontal operculum).

How does taste adapt?

Prolonged exposure to a certain taste reduces sensitivity (e.g., after eating something sweet, other sweet foods taste less intense).

What factors influence taste perception?

Genetics, temperature, culture, past experiences, and smell.

What is supertasting?

Having more taste buds than average, leading to heightened taste sensitivity, especially to bitterness.

What is the relationship between taste and smell?

They combine to create flavor perception; smell contributes more to flavor than taste alone.

What is olfaction?

sense of smell; detection of airborne chemical molecules (odorants)

Where are olfactory receptors located?

In the olfactory epithelium inside the nasal cavity.

How many olfactory receptors do humans have?

Around 350 types of receptors, capable of detecting thousands of odors.

What is the olfactory bulb?

A brain structure located above the nasal cavity that processes smell information before sending it to higher brain areas.

How do odorant molecules trigger smell?

They bind to specific receptor sites on olfactory receptor neurons, generating neural signals.

What is unique about olfactory pathways?

Olfactory signals bypass the thalamus and project directly to the limbic system (amygdala and hippocampus) and orbitofrontal cortex.

Why is smell strongly linked to emotion and memory?

Because it projects directly to the limbic system, which is involved in emotion and memory formation.

What is anosmia?

Loss of the sense of smell, often caused by injury, infection, or age.

What is olfactory adaptation?

Reduced sensitivity to a constant odor over time (e.g., no longer noticing your own perfume).

What is the olfactory cortex responsible for?

Interpreting and identifying odors and their emotional associations.

What is the difference between retronasal and orthonasal olfaction?

Orthonasal = sniffing through the nose; retronasal = odors from food entering the nasal cavity from the mouth during eating.

What role does smell play in flavor

Smell contributes about 75% of flavor perception; without smell, food tastes bland.

What is the somatosensory system?

The sensory system that processes bodily sensations, including touch, pressure, temperature, pain, and body position.

What are mechanoreceptors?

Sensory receptors in the skin that respond to mechanical pressure or distortion.

What are the four main types of mechanoreceptors?

Merkel’s disks, Meissner’s corpuscles, Ruffini endings, and Pacinian corpuscles.

What do Merkel’s disks detect?

Fine touch and texture.

What do Meissner’s corpuscles detect?

What do Meissner’s corpuscles detect?

Light touch and changes in texture (common in fingertips and lips).

What do Ruffini endings detect?

Skin stretch and sustained pressure.

What do Pacinian corpuscles detect?

Deep pressure and vibration.

What is proprioception?

The sense of body position and movement, detected by receptors in muscles, joints, and tendons.

What is kinesthesia?

Awareness of the movement of the body and limbs

What is nociception?

The sensory perception of pain; detection of potentially harmful stimuli.

What are nociceptors?

Sensory receptors that detect pain (mechanical, thermal, or chemical damage).

What are the two main types of pain fibers?

A-delta fibers (fast, sharp pain) and C fibers (slow, throbbing pain).

What is the gate control theory of pain?

Proposes that spinal “gates” regulate the flow of pain signals; psychological and physical factors can open or close these gates

How can pain perception be modulated?

By attention, emotion, expectation, or endorphin release.

What are endorphins?

Natural painkillers produced by the brain that inhibit pain transmission.

What is referred pain?

Pain felt in a location other than its actual source (e.g., heart attack pain felt in the arm).

What is the somatosensory cortex?

The brain region in the parietal lobe that processes touch and body sensations.